patch 9.0.0678: using exclamation marks on :function

Problem:    Using exclamation marks on :function.
Solution:   Use :func and :endfunc as usual.
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index 4181ce8..f28efc9 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -1152,11 +1152,11 @@
   bw!
 endfunc
 
-function! GetPumPosition()
+func GetPumPosition()
   call assert_true( pumvisible() )
   let g:pum_pos = pum_getpos()
   return ''
-endfunction
+endfunc
 
 func Test_pum_getpos()
   new